Navigation instrument



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priority, application France April 9 1951- 15 Claims. (CI. 33-61 v The present invention relatesto instruments for astrolnoniical navigation. The invention provides. an1-mstru States Patent" F trae ment for astronomical navigation including onesor more 1 image-forming devices and two optical image. detectors and. error signal generators which cooperate with-the image-forming device or devices for the simultaneous tracking of two separate. celestial bodies-and for-definino of the. lines of sight thereto, andwhich presents con v tinuous lyand automatically the longitude andlatitudeof. th instrument, which may be. mounted on.- a movingyehiele for example.

,Theipresen't applicationis mminuafioni partcfrour. application Serial No. 278 874, filed .March 27,, I952, nowabandoned'. V i 1 In astronomical. navigation instrument s this type OfQIhe priorart, one'or the other ofitwo separaterheth; ods has been employed to determine. the polaraxis ofithe celestial sphere from astronomical. data obtained by the iastmmem; In one known form ofnavigation'instrument a magnetic. compass is used to. indicate. the North direchon The meridian plane of the position. of .the'i. instru ment is. then determined by the vertical andby'theNor'th. direction. With this plane, which contains the ot the poles, the direction of the polar axis may beld'eten' mined 'with'the help of a'single star-following telescope scope is directed toward the chosen. star, th'e'diiction' ofit's' second axis of rotation is parallel tothe polanaxis'; and the'polar'axis is thus determinedl Anoth'er for'm of instrument heretofore proposedoperateswi thout reliance upon magnetic} compasses; Iriin' strurrients of. this type, the polar axis is' determined by, observing the zenith distances of two celestial bodiesof known declination and by solvingin a computeri'the spherical quadrilateral; the intersections of whose? sides ar efformed bythe zenith pointof'the position of"the i r' strurnent, by the two celestial. bodies, an'dl by one of the unknown poles of the celestial'sphere'. In this quadri la t'eral the four sides and one ofthe angles are known, since the two sides intersecting'at the zenith ofthe instru rhe'nt arequal to the zenith distances of the-two stars and the j two sides intersecting" at. the pole are equal to the complements of the" declinations off these starsi' whereas thejanglebetween the latter two sides isjequal to tliedif frence'b'etween the'right ascensions of thosetwostai's. I n these two types of instrument" it isnecessary that the star-following telescopes berr'rountedonj a horizontally stabilized platform. In view of thec'onsidei-able weight of -the telescopes;v the physical realization" of such a" plato fthe first,

. 2. form is difiicult, and its departures from the horizontal introduce substantialerrors into the data obtained from the instrument. Moreover,.-if there is. to. be achieved independence ofthe magnetic compass element, whose preciti'oaoraagunr indication is muchless than that of optical instruments, itis necessary to provide two star- 'g jtlescopes each having twodegrees of. freedom withr'espect to fixedpart of the instrument. v

7 An object offthe' present invention isto provide an astronomical navigation. instrument giving the longitude and latit' do of a'moving vehicle with precision of the order ofi 'al'minute of arc.- V 1 Anotfierj bject Ofj the present. invention is to' provide an astronomical navigation. instrument including. two o ical acting devices'whose axes of rotation may b1 arljitrar ly chosen; so as to obviate the necessity for a stabilized'hoi-izontal" platform for the mountingofv the devices,, which may for exampletake theformof. telen 7 Another. obje'cfofi the present invention is to provide an astronomical',navigation instrument in. whichone of the twostar tfackingdevicesfis.mountediwith two degrees offfreedom' whereas thesecond, whose axis is. inclined. at a'fixedan e ements of'tlie'fi'rst}.possesses.a single de: gre' offiedblm nan-fier that of rotation about the'axis Xnot "e ohj'ect of the present invention is. to--provide aifastrononiical' navigation instrument which. will indicate automatically and continuously in. addition tothe coordinates of "its' own position the heading and the in clihationwith respect to the horizontal. of the. vehicle. on which it is mounted; these two data being given. with apr e'cision of'tlie order of a minute ofai-cr According to the invention, -.ther'e are selected for tracking" by the two" 'star-trackin'g devi'ces two stars of linown'ang dlar: separationand having a' known angle Between the celestial meridian of one thereof and the great circle passing through the two. These anglesconst'itute 'npitt datafto the'instrument, establishing. an initial ailj'list nt so that" it may correctly operate. on the selcted sta'r's'f v p y I The two star-tracking.devices'comprise each' an. optical. ima e-farming device and a photoelectric detector-sup.- ported at or close to the focal surface of iii'g' device? In some' embodiments of" the invention. a si-ifgl? image forming' devicemfay' be common to both of the star-tracking devices; Qne detector (and, in some Y for rotatioirwith two degreesof freedom, i." e. for two' te'ct'or' (and; in'soni'e embodiments," its associatedimagedetector. Theseconddetector and it'sIimage-forming devicethen definea secohdoptical axis rotatable aboutithe first The second detector can be adjustably fixedfwith as. to incline the two opticalaxes rarer c'e to thefirst' so.

the image-formembodimeht's; its associated image-forming. device); is'

' mounted in' a hase'or other frame ofi'reference is niovably'mounted' with one degree of? i 3 to each other by a desired angle, and an error signal generating apparatus and servosystem adjust the position of the second detector to maintain the optical axis associated therewith parallel to the line of sight to the second star. For convenience each detector with its image-forming device may be referred to as a star-tracking telescope, although as will subsequently appear the combination of detector and image-forming device may depart widely in structure from a telescope in the usual sense. 3

The optical axis of the first of the two star-tracking telescopes is then continuously directed toward the first star, and the optical axis of the second telescope is continuously directed toward the second star. The plane of the telescope axes (i. e. of their optical axes in their object spaces) is physically embodied in an articulated mechanical system linked to the telescopes, and from this plane the meridian plane of the first star is located by a rotation from this plane about the line of sight to that star, the amount of this rotation being equal to the angle between the meridian plane of the first star and the great circle joining the two stars. Lastly in the meridian plane of the first star the direction of the polar axis is determined as the direction which makes with the axis of the first telescope an angle equal to the complement of the declination of the first star.

The invention may be embodied in apparatus of widely differing forms. In particular, the star-tracking devices may be of very diiferent types in different embodiments.

Other objects and features of the instrument of the invention will appear from the following detailed description of a preferred embodiment thereof which is to be talllen in conjunction with the accompanying drawings in w ich:

Fig. 11 is a perspective view of elements which may be included in the instrument of the invention to determine the heading and the inclination with respect to the horizontal of a vehicle in which the instrument of the invention may be mounted;

Fig. 12 is a schematic diagram of the circuits associated with the device of Fig. 11;

Fig. 13 is a perspective view, partly cut away, of an indicator device for presenting the data obtained by the instrument of Figs. 2 to 12;

Fig. 14 is a sectional view on the line 14--14 of Fig. 2 illustrating the frictional drive of the two star-tracking telescopes about one of their two common axes, of rotation with respect to the vehicle in which the instru ment is mounted;

Fig. 15 is a schematic view in side elevation, partly broken away showing a modified instrument embodying the invention, certain elements being omitted for clarity;

Fig. 16 is a perspective view of the instrument of Fig. 15;

Fig. 17 is a fragmentary view of the instrument of Fig. 15, the housing thereof being broken away to show in elevation the primary star light detector and error signal Fig. 1 is a schematic diagram setting forth therprinciples of spherical triangulation upon which the invention is based;

Fig. 2 is a perspective view of an instrument embodying the invention, certain elements shown in other figures being omitted for the sake of clarity;

Fig. 3 is a partial perspective view of a portion of the instrument of Fig. 2 showing the elements of structure by which the data relating to the selected primary and secondary stars are put into the instrument in an initial adjustment, certain elements being again omitted for clarity;

Fig. 4 is a perspective view of a portion of the apparatus shown in Fig. 3, showing in particular the vertical detector and associated elements by which the instantaneous values of the local hour angle of the primary star and the latitude of the instrument are measured; i

Fig. 5 is a view similar to that of Fig. 4 but showing further a portion of certain apparatus which maybe incorporated in the instrument of the invention for the derivation of course and inclination information;

Fig. 6 is a perspective view of one form of device for determination of the vertical direction suitable for use in the instrument of the invention;

Fig. 7 is a schematic representation of the circuit of the vertical direction determining device of Fig. 6, of the servomechanism which adjusts this device with respect to the remainder of the instrument so that it will assume the vertical position, and of remote indicators of its position relative to the remainder of the instrument;

Figs. 8 and 9 are respectively sectional elevation and plan views of a star-tracking telescope suitable for use as the primary star-tracking telescope in the embodiment of the invention shown in Fig. 2, showing in particular photoelectric means effecting automatic tracking of a star thereby. A respective view of a telescope suitable for use as the secondary star-tracking telescope of this embodiment is contained in Fig. 3; i i i Fig. 10 is a schematic diagram of the servomechanisms which control the positioning of the two star-tracking telescopes, together with their associated circuits;

generating system;

Fig. 18 is a fragmentary sectional view taken on the line 18-18 of Fig. 17;

Fig. 19 is a plan view of the light detector and error. signal generator seen in section in Fig. 18;

Fig. 20 is a diagrammatic representation of the control circuits for the slewing motor which cause the primary star-tracking device in the embodiment of Figs. 15 and 16 to follow the primary star; I

Fig. 21 is a diagrammatic view illustrating the control circuits for the slewing motor which causes the secondary star-tracking device in the' embodiment of Figs. 15 and 16 to follow the secondary star;

Fig. 22 is a diagrammatic representation of certain electrical Wave forms useful in explaining the operation of the circuits of Figs. 21 and 22; and

Fig. 23 is a diagrammatic representation of a further modified form of instrument according to the invention.

The principle of position determination employed in the instrument of the invention will now be explained with reference to Fig. 1, which illustrates the celestial sphere. On this sphere Z is the zenith point of the position of the instrument, and A and B are two celestial bodiesor stars to be employed in position determination.

' P and P are the celestial poles, E is the celestial equator and T is the center of the celestial sphere.

The body A, selected as the primary star, is positioned in terms of its right ascension ARA measured along the celestial equator from the vernal point 7 to its own meridian, and in terms of its declination 5A, measured along its meridian from the plane of the celestial equator.

The position of the body B, chosen as secondary star, is determined with respect to the star A by the arc AB of the great circle joining the two and by the dihedral angle BAP between the meridian plane of A and the great circle of arc AB.

The stars to be employed for position determination with the instrument of the invention are preferably chosen among the most brilliant in the heavens, for example among those of magnitude below the first or second magnitudes. Moreover, there should be chosen for the two stars of any pair only stars whose angular separation falls within certain limits dependent upon the desired precision in the results to be obtained. The number of pairs of stars A and B which can be used is consequently limited. For each pairthe arc AB and the angle BAP are computed from the equatorial celestial coordinates of the two stars as obtained from a star catalogue such as the Nautical Ephemeris. The table gives the values of these parameters for several pairs of stars. Of course one can in each of these pairs choose either one or the other of the two stars as the primary star A.

Table Stars I v l BA? is positive in the direct sense A ARA 1 Magni- A'chernar Altair Betelgeuse 2 tude I Acheruar 23 66 147 31 0. 6 AB--- 95 41' 82 54'.

BAR. -s2 41' +64 04'. Altair 297 03 81 17 0. 9 AB--- 95 41 Not usable.

BAR. 147 23' Betelgeuse.. 88 05" 82 36 0. 1 'AB 82 54 Not usable.

' BAP" -o 51' freedom and which will hereinafter sometimes be referred to as the primary star telescope. The line of sight to the secondary star B is determined by a secondary startracking device or telescope mounted in the instrument in such a fashion that its optical axis makes with the axis of the primary star telescope an angle equal to the angle of separation AB of the two stars. Consequently the secondary star telescope is mounted in the instrument with a single rotational degree of freedom.

When the instrument is properlyaligned, as it permanently is when in use, with the twotelescopes pointed at their respective stars, the axislof the primary star telescope determines at every instant the direction.TA. The axis 2 of the secondary star telescope similarly determines at every instant the direction TB. In the instrument of the invention the direction 4 of the axis 7 of the poles PP is determined by rotating about the axis TA the vhalf planeTAB through an angle equal to the dihedral angle'BAP, and by rotating the direction TA in the. plane TAP through an angle equal tothe complement of the. declination 5A. -meridian plane of the primaryv star A, and the second rotation determines the line of direction 4 of the axis of the The first rotation derives the AI-lsz of the star A at the position of Z, i. e. the angle between the meridians of A and Z, the longitude of the instrument is given by the Equation 1.

L=TsoARA-AHAZ (1) In this equation the usual sign conventions are adopted,

for which all the angles shown in Fig. 1 are positive. The latitude will be given by the complement of the angle formed between the vertical direction'TZ and the polar axis.

It is to be noted that in contrast with instruments of the prior art, the star-tracking telescopes are not em-- ployed to introduce into a computer certain astronomical data of the stars being tracked, such as local hour angles or zenith distances. Rather they serve only to define the plane TAB and a direction TA in this plane. Starting from this plane and this direction the polar axis is determined by rotations through known angles which are determined by the stars selected. It is therefore uhnecessary to provide for one or the other of the mechanical axes of the instrument about which the primary star telescope is rotated to keep it on star A, a preferred direction such as the horizontal for example, and it is unnecessary to mount this telescope on a stabilized platfonn. Another advantage of the invention resides in the fact that the secondary star telescope has only a single degree of freedom. The servosystem for controlling the motions of the telescopes is therefore much simplified, and there are avoided the difficulties which follow from a superfluity of input data.

Referring now to Figs. 2, 3, 4 and 5, the primary star telescope 24 is provided with two trunnions 5 and 6 adapted to turn in bearings 7 and 8 formed in a fork 9. These trunnions and bearings define an axis 19. A motor 81 supported on a bracket 11 affixed to the branch 10 of the fork 9 is provided for rotation of the telescope 24 about the axis 19.

Pork 9 is afixed to a shaft 12 which is in turn aflixed to the rotor of a motor 82, fixedly supported at abutments 13 and 14 on a pedestal 75 which is fixed with respect to the vehicle whose position is to be determined.

The shaft 12 is extended on the opposite side of motor 82 by means of a shaft 15 which carries at its end a fork 16 whose plane, as determined by bearings 17 and 18 (Fig. 3) and by the axis of shafts 12 and 15, coincides with that of the fork 9. Bearings 17 and 18 in the for 16 define an axis 24) parallel to the axis 19.

A fork 21 (Figs. 2 and 3) is provided with trunnions 22 and 23 which rotate. in the bearings 17 and 18. Accordingly the fork 21 is free to rotate inside the fork 16. The plane of the fork 21 is maintained parallel to the plane defined by the axis 1 of the telescope 24 and by axis 19 by means of a linkage. comprising the crank pin 26 and connecting rod 25. The connecting rod 25 has a length equal to the separation of the axes 19 and 20,

r and its connection 27 to the fork 21 is separated from the axis 20 by the same distance as that between the crank pin 26 and the axis 19.

The arm 28 of fork 21 is disposed parallel to the axis 20 and is provided with a bearing 29 (Fig. 3) defining an axis 1 lying in the plane of the fork 21. This axis 1' is moreover parallel to the axis 1 of the telescope 24. A shaft 31 is mounted for rotation in the bearing 29 and has aflixed at its upper end a fork 32. The shaft 31 is moreover fastened to the rotor of a motor 83 whose stator is pinned to fork 21. Fork 32 includes bearings 33 and 34 (Fig. 2) defining an axis 126 (Fig. 3) perpendicular to the axis 1'. The secondary star telescope 37 is mounted for rotation about the axis 126 by-rneans of trunnions 35 and 36 (Fig. 2) which engage the bearings 33 and 34. The telescope 37 can be fixed in any desired position with respect to fork 32 such that its optical axis 2 (in the object space) which is always perpendicular to the axis 126, will make the axis 1' an angle equal to the angular separation AB of the stars A and B (cf. Fig. 1). To this end a threaded ring 38 or similar means may be provided about one of the trunnions 35 and 36, adapted to be drawn into frictional engagement with the branch 30 of fork 32. Arm 30 of the fork 32 has afiixed thereto a circular scale 39 with reference to which the angular position of the axis 2 mav be read by means of a pointer 40 affixed to the trunnion 36. Accordingly as shaft 31 turns in bearing 29, the optical axis 2 of the secondary star telescope 37 traces out a cone about the axis 1, i. e. a cone whose axis coincides with the line of sight to the primary star A.

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